In recent years, high definition CCD/CMOS image sensors have been developed and this requires the enhancement of the sensitivity of the sensors. Thus, for microlenses that are loaded in the sensors, high transparency and high heat resistance are required. A conventionally known material for forming microlenses is polyhydroxystyrene. However, there is a room for improvement in the polyhydroxystyrene due to the following disadvantages. In microlenses formed using the polyhydroxystyrene as a forming material, the lens shape is easily changed by heating at high temperatures, so that it is difficult to form microlenses having a stable shape. In addition, such microlenses are easily colored and are likely to have impaired transparency by heating at high temperatures, and thus coloring of such microlenses may be recognized in use.
On the other hand, a photosensitive resin composition is known that is produced using, instead of polyhydroxystyrene, for example, a copolymer having a structural unit derived from maleimide as disclosed in Patent Document 1 and Patent Document 2. It is also known that the composition is used for forming microlenses or insulating films.